The compressor casing (hereinafter referred to as “casing”) of a vertical split type compressor generally includes components such as rotors, blades, and so forth, in the interior thereof. In the casing, which accommodates the components therein, end lids, which are called head, are provided at both ends in the axial direction of the casing. The heads are provided so as to confine the components from both ends in the axial direction of the casing. O-rings for preventing leakage of compressed fluid are provided between the outer circumferential surfaces of the heads and the inner circumferential surface of the casing (see, for example, PTL 1).
As a seal structure using O-rings, PTL 1 discloses a structure in which the O-ring is provided by forming a recessed part on the outer circumferential surface of the head, providing a ring-shaped thin O-ring-retaining ring in this recessed part, and providing an O-ring groove on the outer circumference of the O-ring-retaining ring. In addition, an O-ring groove is also provided on the end surface of the O-ring-retaining ring (the surface orthogonal to the axial direction of the compressor), thereby providing a seal structure for sealing a gap formed with respect to the side surface of the recessed part that is provided on the outer circumferential surface of the head (the surface orthogonal to the axial direction of the compressor).